Programming iOS 6, 3rd Edition

Collection Views

A collection view (UICollectionView), new in iOS 6, is a UIScrollView subclass that generalizes the notion of a UITableView. Like a UITableView, you might well manage your collection view through a UIViewController subclass — a subclass of UICollectionViewController. Like a UITableView, a collection view has reusable cells — these are UICollectionViewCell instances, and are extremely minimal. Like a UITableView, you’ll make the cells reusable by registering with the collection view, by calling registerClass:forCellWithReuseIdentifier: or registerNib:forCellWithReuseIdentifier:, or, if you’ve started with a UICollectionViewController in a storyboard, just assign the reuse identifier in the storyboard. Like a UITableView, a collection view has a data source (UICollectionViewDataSource) and a delegate (UICollectionViewDelegate), and it’s going to ask the data source Three Big Questions:

• numberOfSectionsInCollectionView:
• collectionView:numberOfItemsInSection:
• collectionView:cellForItemAtIndexPath:

To answer the third question, you’ll supply a cell by calling dequeueReusableCellWithReuseIdentifier:forIndexPath:.

As the Three Big Questions imply, you can present your data in sections. A section can have a header and footer, though the collection view itself does not call them that; instead, it generalizes its subview types into cells, on the one hand, and supplementary views, on the other, where a supplementary view is just a UICollectionReusableView, which happens ...